Hey, if you are trying for 2 different sources (tables) then you can use join or data blending .
You can prefer to use joins as the tables have same field names, or else data blending.
If you are using data blending, check if you have the link connected ( RED COLOR ) to establish connection between the 2 tables, then try it will work
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Or else it would show a warning message like this .(here sample - EU Superstore is my data source, if i try to use fields from 2 tables it would pop up a warning)
so try again after connecting try again!!.
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Hope this helps you.